Method for removing weakly acidic substances from substantially neutral organic water-immiscible liquid



Patented Apr. 20, 1943 METHOD FOR REMOVING WEAKLY ACIDIC SUBSTANCES FROM SUBSTANTIALLY NEUTRAL ORGANIC WATER-IMLIISCIBLE LIQUID George W. Ayers, In, Chicago, and Lawrence M.

Henderson, Winnetka, 111., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application June 22, 1940, v

7 Serial No. 341,904

10 Claims.

This invention relates to a method of removing acidic bodies from water immiscible liquids. More particularly, the invention is directed to the problem of removing sulfur compounds from hydrocarbon oils.

Hydrocarbon oils, particularly light distillates resulting from cracking higher boiling fractions frequently contain mercaptans and other acidic sulfur compounds which require removal in or-' der to render the oil .sweet and non-corrosive. It has been common practice in the petroleum refining art to remove part of the sulfur compounds by washing with caustic alkaliand then to sweeten with doctor solution. 7 The disadvantage involved in this type of treatment is that a considerable portion of the sulfur remains in the oil or distillate and adversely affects the antiknock properties of the gasoline. Gasoline con- (Cl. ma-eo) taming sulfur compounds such as organic disulfldes, not only has a lower octane rating than substantially sulfur-free gasoline, but requires much more tetra-ethyl lead to raise its octane rating to a given value.

More recently an improvement in caustic washing for removal of mercaptans and other sulfur compounds has been efiected'by adding to the caustic solution materials such as sodium or potassium isobutyrate, commonly known as solutizers.

We have discovered that the results obtained by washing with caustic alkali solution either alone or containing commercially known solutizers can be considerably improved upon by adding to caustic alkali solution of fairly high concentration a soap or acid, the solubility of which in the alkali solution is low, and a solventizer therefor, i. 'e., a substance which will enable larger quantities of the soap or acid to dissolve in the caustic solution.

Caustic alkali solutions of fairly high concentration will dissolve only relatively small quantities of acid or soaps such as naphthenic acids and hydro-aromatic carboxylic acids and the soaps thereof, and in the quantities that the soap or acid is dissolved in the caustic alkali it has no material eifect insofar as enhancing the ability of the caustic solution to remove acidic substances such as mercaptans and thiophenols from hydrocarbon oils. However, if a material is added having the ability to increase the solubility of the soap or acid in the caustic alkali and a sufiicientlamount of soap or acid is added to the caustic solution, the ability of the caustic to remove mercaptans and other sulfur compounds is greatly enhanced.

On the other hand, caustic alkali solutions of low concentrations will dissolve relatively large amounts of naphthenic or other acids and their soaps, but in low concentrations the caustic alkali solution per se or with addition of the acid or soap is relatively ineffective in removin mercaptans from the oil. If an attempt is made to increase the concentration of the caustic to a point where it is fairly effective in removing mercaptans, the naphthenic acid or other acid soap precipitates out of solution.

Although a number of different compound such as phenols and glycols such as phenol and ethylene glycol can be used as solventizers for the acids and soaps, we have found that those phenols having more than six carbon atoms in the molecule, such as p-, m-, xylenols, o-cresols and alpha-naphthol, and thiophenols such as thiophenol, m-thiocresol and o-thiocresol which per se have the ability to enhance the mercaptan removing ability of caustic solutions, give superior results. The solventizer must be soluble in the resulting solution to the extent of at least 2% by weight of the solution. In order to realize to an appreciable extent the benefits of the invention the solution should contain at least 5% by weight of free caustic alkali, either sodium or potassium hydroxide. The soap or acid is preferably added in amounts ranging from 10%, calculated in terms of equivalent acid, of the caustic solution up to an amount corresponding to the maximum amount of soap soluble in the caustic alkali solution. The amount of solventizer may vary with the particular solventizer and particular soap employed and may be as low solutions.

as 2% by weight of the caustic alkali solution. When using solventizers such as phenol, which have no substantial ability per so when added to caustic solution to enhance the mercaptan extracting ability of the caustic, the amount used should preferably not exceed that amount necessary to dissolve the desired amount of soap in the caustic. But in the case of certain solventizers such as the thiophenols, which in themselves have the ability to enhance the mercaptan extracting ability of caustic solutions, the amounts used may range from the minimum required to dissolve the desired amount of soap up to the maximum amount soluble in the caustic solution. Th combinations of the thiophenols and soaps in caustlc alkali solution of suitable concentration are even more effective than solutions in which a solventizer is used which in itself is not an efiective reagent for removing mercaptans. V

The acids and soaps which have been found to be particularly efiectlve are the naphthenic acids and their soaps. These soaps, as well as others, are preferably added to the caustic solution as the sodium or potassium soap or as the acid per se. When acid is added instead of soap, the soap forms in situ.

A large number of tests were carried out using three commercial samples of naphthenic acid recovered from mineral oils, having the following properties:

Table I A. P. I. gravity at F 14.0 14.8 12.8 Neutralization No. (Mg. KOH

gs: g 240/260 230/235 I. P 260 516 g, 490 i 528 20 604 644 30 510 558 40'? 520 572 so 540 ass 60 e.- 554 504 707 568 618 80 bill 90% 622 E. P 615 624 Per cent recovered 97. 0 97. 0 a. l 622 1 Cracking.

An attempt was made to prepare an aqueous solution oi 40% of naphthenic acids in caustic soda solution of such concentration 01' caustic that the resulting solution would contain 14.6% of tree sodium hydroxide as determined by titration to phenolphthalein end point, using each of the three naphthenic acids above mentioned. A large part 01' the naphthenic acid salt precipitated out of solution as the sodium salt so that in no case did the resulting solution contain as high as 8% of sodium naphthenate calculated as naphthenic acid. The same experience was encountered in an attempt to prepare caustic potash On the other hand, when a small amount 01 phenol or m-cresol or corresponding thio compound was added to the caustic alkali solution, a solution containing 20% to 25% of naphthenate calculated as naphthenic acid was prepared with great ease.

The following table gives the results obtained by treating gasoline prepared by high pressure thermal cracking of a mixture of oil from Van Zandt and Schuler crudes. In the following table, "tree NaOH" and "free KOH" represent N'aOH or KOH present in the solution, determined by titration to a phenolphthalein end point.

- Table II Treating agent (aqueous a.

so utions) m moved tnsatmnne l Caustic soda solution containing 0.77% by weight of NaOH Caustic soda solution containing 0.77% free NaOH, 25% naphthenic acid, sample B (as sodium salt) ustic soda solution containng 14.6% by weight 0! NaOH Caustic soda solution containing 14.6% by weight free NaOB, 26% by weight phe- Camtic soda solutlongonteining 14.6% by weight tree NaOH. 38.7% by weight phen 0.0252

Caustic soda solution containwelght lree yweightpheno], 25% by weight naphthlegic acid (1) (as sodium I so Caustic soda solution contain" ing 14.6% by weight iree NaOH, 8.4% by weightphe- 1101, 25% by weight naph- $165110 acid (2) (as sodium Caustic soda solution containing 14.6% by weight free Na0H,8.3% ywcightphr no], 26% by weight naphthonio acid (3) (as sodium salt 0. 0267 Caustic soda solution containing 14.6% by weight tree NaOH, 13.0% b weight naphthenic acid (1), 13.0% by weight phenol Caustic soda solution containing 14.6% bg weight free NaOH,2.9% yweight phenol, 20.3% by weight naphthenic acid (l) Caiistic poissl iysolution fell]:-

Caustic potash solution contairing 20.5% by weight free KOH, 8.3% by weight phenol, 25% by weight naphgiletljiic acid (1) (as potassium Caustic soda solution containing 14.0% by weight free NaOH, 8.3% by weight mcresol, 25% by weight neph- $0610 acid (1) as sodium Percent Percent 0. 0233 28 'o. ozia Gasoline only slightly doctor sour.

The ioregoing results clearly show that the dilute caustic alkali either alone or in which has been dissolved only naphthenic acid is relatively ineflective to remove merca-ptan sullur Xrom cracked gasoline and that the eflectiveness o. caustic alkali solution oi 14.6% NaOI-I was greater than that 01 the 0.77% caustic solution. Furthermore, caustic potash used in conjunction with the naphthenic acid soaps and solventizer is more en'ective than caustic soda. They also show the u phenol not only does not enhance the mercaptan removing ability of caustic soda, but when added in too large amounts actually detracts from the ability of caustic soda to remove mercaptans and therefore should not be added in larger amounts than necessary. The results further show that with increasing amounts of naphthenic acids in more concentrated caustic alkali solution the ability of the solution to remove mercaptans increases.

In order to determine the eflicacy of the thiophenols in combination with soaps such as those of naphthenic acids in caustic solution a reagent was made by dissolving 20% of naphthenic acid together with 6.7% o-thiocresol in a caustic soda solution, the free NaOH concentration of which was 14.6% by weight after addition of the naphthenic acid and thiocresol. This solution sweetened a sample of cracked gasoline containing 0.0213% mercaptan sulfur prepared from a mixture of Van Zandt and Schuler crudes with one by volume treatment. When the same gasoline was treated with the same volume of a 14.6% caustic soda solution, only 57% of the mercaptan sulfur present in the gasoline was removed and the gasoline was distinctly sour.

Another reagent was prepared by dissolving 10% of o-thiocresol, 10% of m-cresol, and 20% of naphthenic acid (1) in caustic soda solution containing 14.6% free NaOH, and Stoddard solvent, containing 0.0372% of mercaptan sulfur, fractionated from Illinois crude, was treated with the solution. The mercaptan sulfur was lowered to .00l% whereas the treatment of the same Stoddard solvent with straight caustic soda solution containing 14.6% caustic soda removed only 8% of the mercaptan sulfur present. Thus it will be seen that naphthenic acids or soaps thereof when used with solventizers such as the thiophenols which are in themselves effective agents in caustic solution forremoving mercaptans have a much greater ability to remove mercaptans than naphthenic acids in the presence of solventizers which of themselves have little or no effect on mercaptan removal.

When using solventizers of the type which are in themselves effective to enhance mercaptan removal by caustic alkali, it is preferred to use quantities ranging from 5% to 40% by weight of the solution.

It will be apparent that in preparing treating reagents in accordance with the invention, the solventizer may be added as the alkali compound and the soap may be added as such or the acidic components may be added to the alkali solutions and the soap and alkali solventizer compounds formed in situ.

The specific examples given are only by way of illustration and are not intended to limit the invention to the specific quantities given or the particular compounds named. Mixtures of the various solventizers may be used as well as mixtures of diiferent soaps. It is important, however, that sufilcient quantities of free alkali, solventizer and soap be present to obtain the full benefits of the invention.

Although we have found that solutions containing from 5% of free caustic alkali up to the maximum amount soluble in the solution may be used, we prefer to use solutions containing from approximately ill-20% of free sodium hydroxide or 10-40% free potassium hydroxide. The invention also contemplates the use of alcoholic alkali as well as aqueous alkali solutions.

Treating solutions in accordance with this invention can be regenerated in the same manner as caustic alkali solutions, namely, by boiling or by steam stripping, and reused either with or without adjusting the alkali concentration of the solution, and with or without further additions of naphthenic acids and/or phenols.

We claim:

1. In a method for removing weakly acidic substances from substantially neutral organic water-immiscible liquids, the stepwhich comprises contacting, said liquids with an aqueous caustic alkali solution containing at least l0% by weight of free caustic alkali, an amount of alkali metal soap of naphthenic acid substantially in excess of that amount soluble in the caustic alkali solution in the absence of a solventizer and sufllcient to materially enhance the ability of the caustic alkali solution to extract said acidic substances from substantially neutral organic water-immiscible liquids and a sufllcient amount of solventizer to dissolve the soap.

2. The step in accordance with claim 1 in which the solventizer is a glycol.

3. The step in accordance with claim 1 in 6. The step in accordance with claim 4 in which the solventizer is a glycol.

7. The step in accordance with claim 4 in which the solventizer is ethylene glycol.

8. In a method for removing weakly acidic sulfur compounds from hydrocarbon oils, the step which comprises contacting said oils with aqueous alkali metal hydroxide solution containing at least 10% by weight of free alkali metal hydroxide, at least 10% by weight of alkali metal soap of naphthenic acid calculated as acid, said acid having a boiling range of not less than about 475 F. at 10%, to 610 F. at 90% and at least 2% by weight of solventizer.

9. The step in accordance with claim 8 in which the alkali metal hydroxide is sodium hy- GEORGE W. AYERS JR. LAWRENCE M. HENDERSON. 

